1. Field of the Invention
This invention relates to an improvement in easy-open containers provided with a severable tear strip in one end wall thereof and a pull device for initiating severance thereof. The invention particularly relates to lever-type pull devices having both rigidity and flexing endurance. It additionally relates to clad sheet materials having both bending strength and folding endurance and especially relates to aluminum alloy-clad aluminum alloys wherein such bending strength and folding endurance are created and/or enhanced by a selected solution heat treatment and/or aging to a selected temper. It specifically relates to use of such aluminum alloy-clad aluminum alloys for such lever-type pull devices in easy-open containers having means for retaining both the tear strip and the pull tab after severance and means for refastening a retained pull tab to the end wall of the container.
2. Review of the Prior Art
It is common knowledge that beverage containers and the like having an easy-open end wall have become extremely popular, and it is a frequent experience that the rupture-initiating devices therefor, such as sheet-metal rings and elongated tabs, often break when initially bent or when unusual effort is made in order to initiate rupture of an end-wall panel. A solution for such premature tab failure is proposed in U.S. Pat. No. 3,401,823, comprising a reinforced sheet-metal tab formed as a double layer that becomes a three-layer laminate with the can end, whereby the tab is greatly stiffened in its forward portion and the radius of bending is increased.
As a part of the ubiquitous ecological furor, the wide-spread litter and safety problems created by these sharp-edged pull rings, tabs, and the like have been the subject of much adverse comment. As a solution for the throwaway tab problem, a non-detachable tab, having three hingeably attached components, is disclosed in U.S. Pat. No. 3,744,662, preferred materials for this tab being resilient plastic materials such as polypropylene, polyvinyl chloride, nylon, and the like.
As another solution therefor, a co-pending application, Ser. No. 378,448, filed July 12, 1973, discloses a practical easy-open container having a rupture-initiating device which remains attached to the end wall thereof and which is refastenable to the end wall after use, thereby requiring high bending strength and folding endurance. However, this device tends to run squarely into an important practical problem.
The problem arises because tabs requiring high bending strength and bending endurance have customarily been manufactured of steel or other metallic but non-aluminum materials. As a result, if an attempt is made to recycle the entire can, the non-aluminum tab must be removed. The costs of tab removal can readily inhibit recycling for pollution control and raw material conservation.
If an all aluminum-alloy tab could be non-detachably fastened to the end wall of an easy-open can, recycling of the entire can without tab removal would be feasible and economically practicable. However, manufacture of such tabs wholly of aluminum alloys has previously not seemed to be practicable because their low strength and brittleness would greatly aggravate the problem of premature tab failures. Clad aluminum alloys have been suggested for solving many prior art problems requiring high strength, but none are known to have been considered for making rupture-initiating tabs.
Improving the strength of aluminum alloys by heat treatment, cold working, and the like is also well known, and such heat and work treatments have been proposed for creating differential strength properties in some clad aluminum alloys, examples being treatment of aluminum-magnesium-silicon alloys to obtain improved creep resistance at desired static tensile properties in U.S. Pat. No. 3,310,389, manufacture of high-luster aluminum hub caps having high mechanical strength after treating a composite of commercial aluminum alloy clad with high-purity aluminum in U.S. Pat. No. 3,093,459, and fabricating a composite sheet metal panel having layers of different yield strength in U.S. Pat. Nos. 3,354,531 and 3,108,361. However, the art does not teach the treatment of a composite aluminum alloy for increasing both strength and bending endurance thereof.